This application is based on and incorporates herein by reference Japanese Patent Applications No. 2001-96916 filed Mar. 29, 2001 and No. 2001-383520 filed Dec. 17, 2001.
The present invention relates to an AC generator for a vehicle mounted on a passenger car, a truck and the like.
In an AC generator for a vehicle, cooling air is introduced into the sliding contact portion between slip rings and brushes to prevent foreign matters such as water, oil and the like from entering that portion.
In a brush unit disclosed in JP-B2-4-79224, an opening in the axial direction of a cylindrical slip ring cover fitted in a brush holder is closed by a sealing rubber, which has an air passage communicating with the sliding contact portion between the slip ring and the brush. In this structure, the sealing rubber is pressed onto and made to abut against the edge portion of the slip ring cover in an elastically deformed state by a rear cover, thereby securing hermetic sealing around the slip ring.
In this brush unit, because of variations in the shapes of components such as a rear cover, a slip ring cover and the like, the sealing rubber can not uniformly be pressed onto the edge portion of the slip ring cover, so that it is difficult to secure stable hermetic sealing. Further, since the sealing rubber is elastically deformed, an air passage area formed by the sealing rubber is reduced to cause a shortage of cooling air passing through the sliding contact portion between the slip ring and the brush.
In another brush unit disclosed in U.S. Pat. No. 6,294,856 (JP-A-2000-139058), a depression is formed on a brush holder and in which a partitioning portion formed on a slip ring cover is inserted into the depression to form a bent air passage communicating with the sliding contact portion of a slip ring. Since it has a labyrinth structure at the end portion in the axial direction, its size in the axial direction needs to be increased so as to secure a desired amount of suction air, which is contrary to a recent request for a reduction in size.
It is an object of the present invention to provide an AC generator for a vehicle capable of securing sufficient hermetic sealing and a sufficient amount of cooling air around a slip ring and of reducing the size of a brush unit.
According to the present invention, an AC generator for a vehicle has a rotor and a brush unit. The rotor has a rotary shaft, a field winding, and a slip ring provided on one end of the rotary shaft and electrically connected to the field winding. The brush unit has a brush held in sliding contact with the slip ring, a spring for pressing the brush, a brush holder having a portion for receiving the brush, and a slip ring cover for covering the outer periphery of the slip ring. An air suction/discharge port is formed in a peripheral direction of the slip ring cover. With the suction/discharge port thus formed, when the brush unit is assembled into the AC generator, it is possible to prevent the suction/discharge port from being deformed and thus an air passage area from being reduced, which results in securing a sufficient amount of cooling air.